Update bower.json for Polymer elements and add PRESUBMIT.py

third_party/polymer/v1_0/components/iron-collapse/iron-collapse.html

 <!--
 @license
 Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 Code distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
 
@@ skipping 93 matching lines @@
         type: Boolean,
         value: false,
         notify: true,
         observer: '_openedChanged'
       }
 
     },
 
     hostAttributes: {
       role: 'group',
-      'aria-expanded': 'false',
-      tabindex: 0
+      'aria-expanded': 'false'
     },
 
     listeners: {
       transitionend: '_transitionEnd'
     },
 
     ready: function() {
       // Avoid transition at the beginning e.g. page loads and enable
       // transitions only after the element is rendered and ready.
       this._enableTransition = true;
@@ skipping 61 matching lines @@
     },
 
     _calcSize: function() {
       return this.getBoundingClientRect()[this.dimension] + 'px';
     },
 
 
   });
 
 </script>